A prior art motor vehicle is equipped with a fuel vapor treatment system that causes fuel vapor generated in a fuel tank to be adsorbed and temporarily kept on a canister and supplies the adsorbed fuel vapor into an air intake system of an internal combustion engine to be burned out by the internal combustion engine. A proposed structure of the fuel vapor treatment system includes a sealing valve located between the fuel tank and the canister and a pump located between the canister and the air intake system of the internal combustion engine. For example, a known fuel vapor treatment system disclosed in Japanese Patent Laid-Open Gazette No. 2004-156492 opens the sealing valve during fueling, causes the fuel vapor generated in the fuel tank to be adsorbed on the canister, and controls the internal combustion engine to burn out the adsorbed fuel vapor after a start of the motor vehicle. This system prevents leak of the fuel vapor from a filler neck of the fuel tank during fueling. The prior art motor vehicle also has a function of executing leak diagnosis. The leak diagnosis actuates a pump to introduce a negative pressure into a pathway connecting the fuel tank to the air intake system of the internal combustion engine after elapse of a preset time period since a stop of the motor vehicle and specifies the presence or the absence of any leak hole of the fuel vapor in the pathway, based on a pressure change in the pathway.
In the prior art motor vehicle, the fuel vapor treatment and the leak diagnosis require activation of the fuel vapor treatment system and actuation of the sealing valve and the pump. A supply of electrical energy from an accumulator unit, such as a battery, is generally consumed for activation of the fuel vapor treatment system and actuation of the sealing valve and the pump. Continuation of the fuel vapor treatment and the leak diagnosis in a low state of charge of the accumulator unit may cause an insufficiency of electrical energy and interfere with a start of another required operation of the hybrid vehicle with a supply of electrical energy from the accumulator unit.